The objective of the proposed program is to gain an understanding of the molecular basis of tissue specific intercellular adhesion. Attention is focused on the adhesive properties of embryonic, adult, and neoplastic liver cells from chick, rat, and mouse. The adhesive specificity of these cells has been studied using a specific cell adhesion assay (collecting aggregate assay). A clear organ and species specificity for liver cell:cell adhesion has been discovered. Other studies are directed at the identification, isolation, and characterization of the tissue specific cell ligands responsible for adhesive specificity. Liver cell plasma membranes are being isolated to gain insight into the functional integration of these molecules within this organelle. Elucidation of the chemical basis of ligand interactions (protein:protein, protein:carbohydrate) underlying cell-to-cell interactions involved in morphogenesis, differentiation, and tissue homeostasis is the long range of this program.